Additives for water-resistant gypsum products

ABSTRACT

Emulsions are provided which are useful in imparting water-resistance to gypsum products. In one embodiment, the emulsions comprise at least one wax, an alkyl phenol, a salt of polynaphthalenesulfonic acid, and a complexed starch. Emulsions of this embodiment may be added to hot, even boiling, water without the emulsion separating or curdling. The emulsions of the present invention are stable for extended periods of time when stored at room temperature and do not require the addition of a bactericide. The emulsions of the present invention are pourable liquids at room temperature.

This application claims the benefit of U.S. Provisional Application No.60/417,770, filed 11 Oct. 2002, and U.S. Provisional Application No.60/454,168, filed 12 Mar. 2003.

FIELD OF THE INVENTION

The present invention relates to an additive useful in improving thewater-resistance of gypsum products. The present invention also relatesto an emulsion which includes a wax or a combination of waxes, an alkylphenol, a salt of polynaphthalenesulfonic acid, and a complexed starch,the emulsion useful in improving the water resistance of gypsumproducts. The present invention further relates to a method of makingthe emulsion.

BACKGROUND OF THE INVENTION

Certain properties of gypsum (calcium sulfate dehydrate) make it verypopular for use in making industrial and building products; especiallygypsum board. It is a plentiful and generally inexpensive raw materialwhich, through a process of dehydration and rehydration, can be cast,molded or otherwise formed to useful shapes. The base material fromwhich gypsum board is manufactured is the hemihydrate form of calciumsulfate (gypsum), commonly termed stucco, which is produced by the heatconversion of the dihydrate from which the water phase has been removed.

In the making of gypsum board, the gypsum slurry must flow onto a papersubstrate. In a continuous process, the slurry/substrate combination isthen sized by passing this combination between rollers. Simultaneouswith this sizing step, a paper backing is positioned over the sizedgypsum slurry. Accordingly, the gypsum slurry must possess sufficientfluidity so that a properly sized gypsum board can be made. Fluidityrefers to the ability of the gypsum slurry to flow.

It is also important to the manufacture of gypsum board, that the gypsumslurry be capable of being foamed to a limited extent. Foamabilityrefers to this ability to be foamed. When the gypsum slurry and papersubstrate are passed though the sizing rollers, a certain amount of thegypsum slurry must back flow and accumulate in the rollers nip so that asteady flow of gypsum is delivered to the sizing rollers. Foamability isimportant to this ability of the gypsum slurry to back flow at therollers nip. Forming plates may be used, eliminating the use of a masterroll, but foam is important to control density of the finished product.

Because of the continuous nature of a gypsum board manufacturing processwherein the gypsum slurry flows onto a substrate which then passesthrough sizing rollers, the extent to which the gypsum slurry flowsafter it is sized is critical to maintaining the finished productdimensions of the gypsum board. The time at which the gypsum slurryceases its flow is referred to as the pre-set time. Therefore, pre-settime is an important property of the gypsum slurry. The set time of thegypsum slurry is also an important property. The set time refers to theamount of time it takes the gypsum slurry to be dried, under heat, tothe finished, solid gypsum board. As is well known in the art, in acontinuous gypsum board manufacturing process, it is important that thegypsum slurry possess a consistent set time.

Gypsum board absorbs water, which reduces the strength of the wallboard.Prior art products, like ordinary gypsum board, gypsum tile, gypsumblock, gypsum casts, and the like have relatively little resistance towater. When ordinary gypsum board, for example, is immersed in water,the board quickly absorbs a considerable amount of water, and loses agreat deal of its strength. Actual tests have demonstrated that when a 2inch by 4 inch cylinder of gypsum board core material was immersed inwater at about 70° F., the cylinder showed a water absorption of 36%after immersion for 40 minutes.

Previous attempts to provide water-resistant properties to gypsum boardinclude incorporation of asphalt, metallic soaps, resins, and waxadditives into a aqueous gypsum slurry. The resulting materials weredifficult to use and the core properties difficult to control.Polysiloxane-based systems have also been used in attempts to impartwater-resistance to gypsum board. However, the polysiloxane-basedsystems are both expensive and difficult to use. A finished gypsumproduct has also been coated with water-resistant films or coatings. Onespecific example of a past attempt to provide a water-resistant gypsumproduct is the spraying of a molten paraffin, wax or asphalt into anaqueous gypsum slurry.

Another example of a prior art attempt to provide a water-resistantgypsum product is the addition of an emulsion of wax, such as paraffinwax, and asphalt, in the relative proportions of from about 1 part toabout 10 parts of asphalt per part of wax to the aqueous gypsum slurry.Since the asphalt is a relatively poor solvent for paraffin wax andsimilar wax at ordinary temperatures, the solution formed at hightemperatures tends on cooling to deposit microscopic wax crystals on theasphalt-wax surface.

Polyvinyl alcohol has been used in an attempt to provide a roomtemperature system for use in adding water-resistant properties togypsum. However, the polyvinyl alcohol system tends to rapidly separateand thus typically requires continuous mixing prior to use. The inherentinstability of the polyvinyl alcohol systems tends to producestratification of the compounds in the formulation. Therefore, thepolyvinyl alcohol systems tend to be compositionally inconsistent. Inaddition, because of destabilization into different phases, there isalso the potential for bacterial growth.

Accordingly, there is a need for an additive which is useful inimparting water-resistance to gypsum products, and which is economicalto apply. There is a need for a water-resistance additive which does notrequire the use of costly components such as polysiloxane. There is aneed for a stable, water-resistance additive. There is a further needfor a water-resistance additive which is stable at room temperate andwhich does not require heating prior to application to a gypsumsolution. There is still a further need for a stable water-resistanceadditive which does not require continuous mixing or agitation tomaintain its stability. There is yet a further need for a stablewater-resistance additive which does not require the addition of abactericide to control bacterial growth inherent in existing systems. Ofcourse, such additives should perform these functions without affectingfluidity, foamability, pre-set time or set time.

Historically, products added to a gypsum slurry to impart a degree ofwater-resistance in the board manufacturing process have incorporatedasphalt, molten wax, emulsified wax/asphalt, emulsified wax, and varioussilicone products. These prior art systems have all demonstratedshortfalls in any number of performance related areas. These shortfallsinclude, but are not limited to, inconsistent solids, instability of theemulsions, wide ranges in apparent viscosity, a caustic pH requiringhazardous labeling, health risks due to the evolution of hydrogen andhydrogen sulfide gases. An additive is needed that can address theaforementioned issues and impart water-resistance to a product.

It has been noted in earlier work that the incorporation of a genericstarch species from corn, sago, wheat, rice, etc., with a complexingagent such as sodium borate in combination with other chemicalcompounds, specifically sodium lignosulfate, and C₂₄ and greaterpolymerized alkyl phenol and various waxes forms a nearly stable waxemulsion suitable for incorporation into a gypsum slurry to impartwater-resistance. While this system shows significant advantages overpreviously available wax emulsions it to suffers from a number ofdeficiencies, including: degradation of the pH due to bacteriologicalactivity resulting from the decomposition of the sodium lignosulfate inlong-term storage, viscosity changes as temperature and age occurmanifesting itself as a slight separation at the water/wax interface,and less than predictable use rates at the mixer due to the changesoccurring singularly and in combination.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide an additive emulsion and amethod for making the emulsion that addresses the issues of waterabsorption, viscosity control, stability, and slurry fluidity.

In one embodiment, the present invention provides an emulsion includingat least one wax, an alkyl phenol, a polynaphthalenesulfonic acid, analkali metal hydroxide, and a complexed starch. Thepolynaphthalenesulfonic acid and the alkali metal hydroxide react togive a salt of polynaphthalenesulfonic acid. Emulsions of thisembodiment may be added to hot, even boiling, water without the emulsionseparating or curdling. The emulsions of the present invention arestable for extended periods of time when stored at room temperature anddo not require the addition of a bactericide. The emulsions of thepresent invention are pourable liquids at room temperature. Theemulsions of the present invention are useful in providingwater-resistance to a gypsum product.

In another embodiment, the present invention provides a method formaking an emulsion, including the steps of:

(a) mixing at least one wax and an alkyl phenol to provide a firstpre-mix;

(b) mixing polynaphthalenesulfonic acid, an alkali metal hydroxide,water, and a complexed starch to provide a second pre-mix;

(c) combining the first pre-mix and the second pre-mix to provide amixture; and

(d) homogenizing the mixture.

The emulsions of the present invention are useful in providingwater-resistance to a gypsum product.

The emulsions of the present invention are useful in impartingwater-resistance to gypsum products. The emulsions of the presentinvention may also include a fire retardant. The emulsions of thepresent invention may be used in the manufacture of conventional gypsumboard, composites made using gypsum, such as gypsum/fiber composites,and other gypsum products.

DETAILED DESCRIPTION OF THE INVENTION

There is provided in accordance with the principles of the presentinvention an emulsion which is useful in imparting water-resistanceproperties to gypsum products. The emulsions of the present inventionmay be added to mixtures of gypsum and water without adversely affectingproperties of the mixture which are necessary to the manufacture ofgypsum products such as gypsum board. Such properties include fluidity,foamability and set time.

In the manufacture of gypsum wallboard products it is important toimpart water-resistance to the finished product, so as to limit themaximum water absorption realized by the wallboard in a defined boardsoak test. For example, American Standards for Testing Materials ASTM1396 and sub parts thereof describe such a test.

It has been found that the generic starch compounds used in earlier workrequire cooking time temperatures to reach a gelation state at which aparticular viscosity is achieved. It has further been noted that theinitial viscosity moves through and continues to move through a numberof ranges influenced by storage conditions and additive chemistry. Thiscontributes to the unpredictable nature of these systems. It has beendiscovered that by utilizing starch compounds such as acid-modified,hydroxyethylated, oxidized, and/or cationic, in combination with acomplexing agent and a salt of polynaphthalenesulfonic acid coupled witha polymerized alkyl phenol all in a correct relationship, that the noteddeficiencies are corrected and a resulting wax emulsion having superiorperformance as a water absorption control additive is achieved. Thesenewly discovered combinations provide a higher level of stability bothat high temperature and low temperature, provide an unchanging andpredictable viscosity, eliminate the need for the addition of biocides,needed in the former systems to control bacteriological activity, andprovide an even higher level of water-resistance over other additiveproducts.

It has further been discovered that borate compounds, molybdatecompounds, and molybdenum compounds are surprisingly effectivecomplexing agents. Examples of useful complexing agents include, but arenot limited to, sodium borate (borax), magnesium borate, and otherborate compounds; ammonium molybdate, sodium molybdate, magnesiummolybdate, and other molybdate compounds; molybdenum disulfide and othermolybdenum compounds.

The ratio of complexing agent (for example, sodium tetraboratedecahydrate, sodium molybdate dihydrate, molybdenum disulfide, or othercompounds) to the modified starch significantly influences the controlof other necessary properties in the board/slurry process, i.e. foamsupport and slurry additive compatibility. This newly discoveredchemistry eliminates the need for the sodium lignosulfate previouslyused as both a cosurfactant and a dispersing aid which thereforeeliminates the need for a biocide to control biological activity.

It has further been discovered that these combinations and the ratiosthereof are unique and necessary to formulate a stable and performingwax emulsion and that certain manufacturing processes must occur. Therange of ratios of starch:borate, or starch:molybdate, or starch:molybdenum compound may range from about 4:1 to about 20:1 on aweight/weight basis.

Water, a complexing agent (that is, a borate compound, a molybdatecompound, or a molybdenum compound) and a starch are first broughttogether in order to make the complexed starch useful in embodiments ofthe present invention. Next, polynaphthalenesulfonic acid and potassiumhydroxide are added to the aqueous solution of completed starch. Thismixture is brought to a temperature of about 185° F. to about 205° F.and held until the starch reaches its maximum state of gelation, whichtypically occurs in about 20 to about 30 minutes. The wax compounds areincorporated with the polymerized alkyl phenol and brought to atemperature of about 185° F. to about 205° F. Then, the wax phase isadded to the water phase and reacted to form an in situ surfactant. Adetergent/dispersant is formed by the combination and reaction of thepolymerized alkyl phenol and the polynaphthalenesulfonic acid, whichacts to modify the wax crystal and allows the wax crystals to resistplating and linking with themselves and instead remain in adisassociated state until they are transferred due to polarity to thegypsum. The reacted system is then passed through a homogenizer at apressure of about 2,000 to about 4,000 psi and then cooled at aprescribed rate to control the stability and viscosity of the finishedwax emulsion. The homogenized composition exits the homogenizer at atemperature of about 135° F. to about 145° F. The mixture is then cooledto about 80° F. to about 110° F. The cooling rate is controlled to avoidcausing the wax to recrystallize and breakout of solution.

The incorporation of the polynaphthalenesulfonic acid promotes anegative charge to the gypsum crystal thus providing an active site forthe wax to align and coat providing the water-resistant properties.Further, it is discovered that by utilizing the modified starchcompounds in combination and proper ratios with other noted compounds,that a low viscosity system can be developed allowing a broader range ofsolids, from about 40% to about 60% by weight to be available andusable.

Preparation of Emulsions:

Emulsions were prepared by heating the wax and surfactants (“waxmixture”) in one vessel and the water, complexing agent (a boratecompound, a molybdate compound, or a molybdenum compound) and cornstarch (“water mixture”) in another vessel. Both mixtures were heated,with mixing, to about 185° F. (85° C.). Next, the wax mixture was pouredinto the water mixture under mixing. The resultant mixture was thenplaced in a homogenizer. With homogenization it is preferred that adistribution of micelle diameters ranging from about 0.6 micron to about1.8 micron be achieved. However, the distribution of micelle diametersmay range from about 0.5 micron to about 2.5 micron. This level ofhomogenization may be attained, for example, by using a dual orificehomogenizer operating at from about 2,000 to about 4,000 psig.

It is preferred that the homogenized mixture be cooled after thehomogenization step. It is most preferable that the homogenized mixturebe cooled from approximately 185° F. to about 100° F. This may beaccomplished by running the homogenized mixture through a cooling coilimmersed in water maintained at room temperature.

HLB Values:

The hydrophilic/lipophilic balance (“HLB”) value describes therelationship of a compound to its solubility in water. An emulsifierhaving a low HLB value will tend to be oil soluble and one having a highHLB value will tend to be water soluble. Typically, a water solubleemulsifier or blends thereof are used to make an oil/water emulsiontypical of those described herein, or to solubilize oils or waxes, or toobtain some measure of detergent action. Thus, the HLB value can be usedto describe or select the proper emulsifier or emulsifier system.

Where two or more components are combined, the HLB value of thecombination is the weighted average of the individual HLB values. Thefollowing formula may be used to calculate the HLB value of acombination of materials:

${{{HLB}({combined})} = \frac{{Q_{1} \times \left( {HLB}_{1} \right)} + {Q_{2} \times \left( {HLB}_{2} \right)} + {\ldots\mspace{11mu} Q_{n} \times \left( {HLB}_{n} \right)}}{Q_{1} + Q_{2} + {\ldots\mspace{11mu} Q_{n}}}};$where,

-   -   Q₁=weight of material 1; HLB₁=HLB value of material 1    -   Q₂=weight of material 2; HLB₂=HLB value of material 2    -   Q_(n)=weight of material n; HLB_(n)=HLB value of material n        Test Specimens:

Test specimens were made by mixing 50 grams of gypsum, 35.97 grams ofwater, and 1.92 grams of a specified emulsion. For the control, noemulsion was added. Gypsum, water and, if added, emulsion, were mixedtogether and left to stand for one minute. This mixture was then mixedfor an additional 30 seconds. After this second mixing, the specimenswere subjected to fluidity testing.

Fluidity Test:

The specimens mixed as provided above were poured out onto a flatsurface and the diameter of the resulting patty was measured. Thediameter of a patty is an index of the fluidity of the specimen. Thelarger the diameter, the more fluid the specimen.

Foamability Test

The foamability test is used to determine the affect of a wax emulsionon the stability of foam in a gypsum slurry. In this test, 0.60 grams ofa commercially available foamant and 2 grams of wax emulsion are weighedout. The foamant and the emulsion are placed into a blender along with100 grams of water. The mixture is blended for 20 seconds. At the end ofthis blending step, the foam is immediately poured from the blender cupinto a tared 150 ml beaker to overflowing. Any excess is struck off thebeaker. Any foam remaining in the blender cup is set aside. The foamdensity is determined by weighing the foam in the 150 ml beaker. Twominutes after the blending has stopped, any liquid in the remaining foamin the blender cup is drained and discarded. A clean, tared, 150 mlbeaker is filled with the remaining foam to overflowing and the excessis struck off. A second foam density is determined as described above.For the emulsions of the present invention, foam densities wereacceptable and ranged from about 40 to about 65 grams per 150 ml, forthe measurements made at 20 seconds, and from about 10 to about 45 gramsper 150 ml, for the measurements made at 2 minutes.

Water Absorption Test:

Patties made in the Fluidity Test were dried for at least 24 hours at110° F. At the end of this time, the patties were weighed and the weightwas recorded. The dried patties were then immersed in water for twohours. At the end of the two hour immersion, the patties were weighedand this wet weight was recorded. Percent water retention was thencalculated based on the difference between these two recorded weights.

Materials:

Various sources of gypsum may be used in the compositions of the presentinvention. However, the amount of water required to hydrate a gypsumsample will vary with the purity of the sample.

Waxes useful in making the various embodiments of the present inventionmay be selected from any of the commercially known waxes which have amelting point of from about 120° F. to about 150°, and preferably fromabout 135° F. to about 145°. Such waxes are typically of low volatility,exhibiting less than about a 10% loss in weight during standardthermogravimetric analysis. Also, the oil content of these waxes istypically less than about 1% by weight. These waxes are of a relativelyhigh molecular weight, having an average chain length of C₃₆, that is a36 carbon chain length, or greater.

In certain embodiments, it is useful to saponify one or more of thewaxes. In this way, the saponified wax functions as an added surfactant.Waxes useful in this respect are limited to waxes having an acid valueor a saponification value and a melting point greater than about 180° F.Saponification of such waxes may be accomplished by combining the waxwith a strongly basic material such as sodium hydroxide or potassiumhydroxide. Waxes which may be saponified in the emulsions of the presentinvention include montan wax, carnauba wax, beeswax, bayberry-myrtlewax, candelilla wax, caranday wax, castor bean wax, esparto grass wax,Japan wax, ouricury wax, retamo-ceri mimbi wax, shellac, spermaceti wax,sugar cane wax, wool-lanolin wax, and others. The amount of stronglybasic material needed to saponify a wax may be calculated based on thesaponification value of the wax. For example, the saponification valuedivided by 1000 equals the grams of potassium hydroxide to add per gramof wax.

Starch used in the emulsions of the present invention is complexedstarch. The starch may be complexed in situ, during manufacture of theemulsion, or the starch may be pre-complexed prior to being added to theemulsion. Starch is preferably complexed by mixing the starch with acomplexing agent such as a borate compound, a molybdate compound or amolybdenum compound. For example, a preferred borate compound is sodiumtetraborate decahydrate. For example, a preferred molybdate compound isammonia hepta molybdate. For example, a preferred molybdenum compound ismolybdenum disulfide. Other compounds useful in complexing starchinclude ammonium biborate, ammonium pentaborate, potassium pentaborate,potassium tetraborate, lithium tetraborate, and magnesium boratecompounds; ammonium dimolybdate, ammonium heptamolybdate, bariummolybdate, calcium molybdate, lithium molybdate, magnesium molybdate,sodium molybdate, and potassium molybdate; and other molybdenumcompounds, and the like. The starch useful in making the complexedstarch of the present invention includes, but is not limited to, corn,rice, wheat, potato, sago and other starches. The ratio of complexingagent (a borate compound, a molybdate compound, or a molybdenumcompound) to starch is important to the functionality of the complexedstarch in the emulsions. It has been found that the ratio may be as lowas 1:20, of complexing agent (a borate compound, a molybdate compound,or a molybdenum compound) to starch on a weight per weight basis. Theratio may be as high as 1:3.5, however it has been found that at thisratio, and higher ratios, a greater amount of complexed starch is neededin the emulsion to maintain the balance of desired properties in thegypsum mixture and final gypsum product. These desired propertiesinclude fluidity, foamability, and water-resistance.

Incorporating alkyl phenols into the emulsions has been found importantto achieving low water absorption in the final gypsum product. As usedherein, “alkyl phenols” refer to phenolic compounds having a long chainalkyl group. The long chain alkyl group may be straight or branched. Thelong chain alkyl group may be C₂₄-C₃₄ (from 24 to 34 carbon chainlength). Such alkyl phenols include long chain, C₂₄-C₃₄ (from 24 to 34carbon chain length) polymerized methylene-coupled alkyl phenol, phenatesalts, calcium phenates, long branched chain calcium alkyl phenols, longstraight chain calcium alkyl phenols and complex polymers of maleic acidwith and without an amine group substitution. One example of an alkylphenol useful in the compositions of the present invention is describedbelow.

Identification No. Description Source 319H C₂₄-C₃₄ polymerizedmethylene- Lubrizol Chem. Corp. coupled alkyl phenol Wycliffe, Ohio

In certain embodiments which use a single wax additive, it has beenfound that a dual surfactant system provides a stable emulsion at bothroom temperature and elevated temperatures. Such stable emulsions may beadded, for example, to hot or boiling water, without the emulsionseparating or curdling. The dual surfactant system uses a unique ratioof the component surfactants to provide an HLB value within a range ofabout 8.9 to about 14. It is preferred that the component surfactantseach have an HLB value greater than 6. One example of a dual surfactantsystem of the present invention is a combination ofdodecylisopropanolamine benzene sulfonate and a nonionic ethoxylatedaryl phenol. Dodecylisopropanolamine benzene sulfonate may be obtainedfrom Unichema, Wilmington, Del., under the trade name SD1121. Onenonionic ethoxylated aryl phenol is Ethox 2938, available from EthoxCorp., Greenville, S.C. Alternatively, an alkoxylated fatty acid estermay be combined with the of dodecylisopropanolamine benzene sulfonate toform the dual surfactant system. One alkoxylated fatty acid ester isEthox 2914, also available from Ethox Corp., Greenville, S.C.

It has also been found that in certain embodiments of the presentinvention a dispersing aid, or fluidity modifier, is useful for themaintenance of the fluidity of the gypsum/emulsion mixture. Suchdispersing agents are strong lipophiles, which are, consequently, gooddefoamers. One such dispersing agent is poly(oxy-1,2-ethanedyl),alpha-phenyl-omega-hydroxy styrenate.

Bactericides/fungicides can be included in the present invention. Anexample of a bactericide fungicide is METASOL D3TA, which is3,5-dimethyl-tetrahydro-1,3,5,2H-thiadiazine-2-thione. METASOL D3TA maybe obtained from Ondo-Nalco, Houston, Tex.

A salt of polynaphthalenesulfonic acid is required by the presentinvention. An example of a polynaphthalenesulfonic acid is DISAL GPS.The polynaphthalenesulfonic acid and an alkali metal hydroxide arereacted to give a salt of the polynaphthalenesulfonic acid. DISAL GPSmay be obtained from Handy Chemical, Montreal, Quebec, Canada.

Wax Emulsions Including Polynaphthalenesulfonic Acid

An emulsion can be formed by combining and homogenizing at least onewax, an alkyl phenol, a salt of polynaphthalenesulfonic acid, and acomplexed starch. Table 1 below provides examples of emulsions madeaccording to this embodiment. Also, there is provided results of testingthe gypsum/emulsion mixture and gypsum product. All mixtures andhomogenizations were made, and tests were performed, as described above.

TABLE 1 WAX EMULSIONS INCLUDING POLYNAPHTHALENESULFONIC ACID Component/(amount of Component, % by wt) Parameter Emulsion A Emulsion B EmulsionC Emulsion D Wax 3816D 33.00 33.00 36.00 38.00 Montan Wax 3.30 3.30 3.603.80 Alkyl Phenol 0.50 0.50 0.50 0.50 DISAL GPS 1.00 1.00 1.20 1.50Water 59.50 59.10 55.58 52.97 Borax 0.37 0.37 0.37 0.37 Acid-modified1.60 1.60 1.60 1.60 C150 Starch 45% KOH 0.75 0.75 0.818 0.864 METASOL0.40 0.40 0.40 D3TA % Water 0.5-5.0 0.5-5.0 0.5-5.0 0.5-5.0 Absorbed

The emulsions of Table 1 were mixed with water and gypsum is added tothe water emulsion mixture. The water/emulsion/gypsum mixture is thenformed into a test specimen as described above. The standard testspreviously described are used to evaluate the properties of the testspecimen. For example, test specimens were tested for percent waterabsorption and the range of values provided in Table 1 were measured. Inaddition, similar emulsions can be made using molybdate compounds ormolybdenum compounds as a complexing agent, replacing the Borax usedabove.

Typical composition ranges for the compositions of the present inventionare provided in Table 2 below.

TABLE 2 TYPICAL COMPOSITION RANGES Component Typical Amount (% weightbasis) First Wax 25-40 Saponifiable Wax 2.5-4.5 Alkyl Phenol 0.25-10.0Polynaphthalenesulfonic Acid 0.25-5.0  Water 55-65 Starch + ComplexingAgent 1.5-3.5 (4:1 to 20:1) Alkali Metal Hydroxide Amount used dependson amount of saponifiable wax; typically 0.5-1.5Comparative Multiple Wax Systems:

An emulsion can be formed by combining and homogenizing two waxes, aco-surfactant, an alkyl phenol and a complexed starch. Table 3 belowprovides examples of emulsions made according to this embodiment. Also,there is provided results of testing the gypsum/emulsion mixture andgypsum product. All mixtures and homogenizations were made, and testswere performed, as described above.

TABLE 3 COMPARATIVE MULTIPLE WAX SYSTEMS (amount of component, grams)Control Component/ (no Parameter Emulsion E Emulsion F Emulsion Gemulsion) Wax 3816 134.0 132.0 130.0 Montan Wax 12.0 12.0 12.0 319H 10.04.0 6.0 Sodium 4.0 4.0 4.0 lignosulfonate Water 239.0 237 237 Borax 1.51.5 1.5 Corn Starch 6.5 6.5 6.5 KOH 3.0 3.0 3.0 % Water Retained 1.077.76 −0.34 33.30 Fluidity 3 inches 3.25 inches 3.25 inches 4 inches

Wax 3816 is a hard paraffin wax, available from Honeywell/Astor, Duluth,Ga. In the emulsions described in Table 3, corn starch is complexed withsodium tetraborate decahydrate. Montan wax was saponified in situ by theaddition of potassium hydroxide (KOH). Alternatively, the complexingagent can be another useful borate compound, or a molybdate compound ora molybdenum compound.

Comparative Single Wax Systems

An emulsion can be formed by combining and homogenizing a single wax, adual surfactant system, an alkyl phenol and a complexed starch. Table 4below provides examples of emulsions made according to this embodiment.Also, there is provided results of testing the gypsum/emulsion mixtureand gypsum product. All mixtures and homogenizations were made, andtests were performed, as described above.

TABLE 4 COMPARATIVE SINGLE WAX SYSTEMS Component/ (amount of component,grams) Parameter Emulsion J Emulsion K Emulsion L Control Wax 3816 135.0134.5 134.5 319H 4.0 4.0 4.0 Ethox 2914 14.0 12.0 12.0 SD1121 4.0 4.04.0 Water 240.0 240.0 240.0 Borax 0.5 0.5 0.5 Corn Starch 2.5 5.0 5.0 %Water 1.24 −0.02 3.47 33.30 Retained

As illustrated in Table 4 above, a combination of a single wax, a dualsurfactant system, an alkyl phenol and a complexed starch significantlyreduces the amount of water absorbed by the gypsum product.Alternatively, the complexing agent can be another useful boratecompound, or a molybdate compound or a molybdenum compound.

The use of borates or trisodium phosphate in emulsions imparts twoadditional benefits to the gypsum products employing such emulsions. Forexample, borates and trisodium phosphate are useful as fire retardantcompounds and these compounds are natural biocides. Therefore,incorporation of a fire retardant compound into a gypsum product canpresent certain advantages to the users of these gypsum products. Also,the emulsions of the present invention do not require the furtheraddition of another biocide to prevent bacterial growth in theemulsions.

Table 5 illustrates performance advantages achieved with certainembodiments of the present invention. Water absorption tests wereperformed according to the procedures described above.

TABLE 5 EXPERIMENTAL RESULTS Molybdate or Molybdenum Compound or Blank %Water Absorption Blank 27.61 Sodium Molybdate Dihydrate 4.30 AmmoniumHeptamolybdate −0.09 Ammonium Dimolybdate 4.33 Molybdenum Disulfide−0.05

The experimental results demonstrate an improved emulsion for use ingypsum compositions. The improved emulsion unexpectedly reduces theamount of water absorbed by test specimens by an order of magnitude.Through the use of a polynaphthalenesulfonic acid, lignin compounds andbiocides can be eliminated from gypsum formulations. The elimination ofthese two compounds improves the manufacture and cost of the gypsumcompositions using the emulsions of the present invention.

There has been disclosed in accordance with the principles of thepresent invention an emulsion and gypsum product made using such anemulsion. The emulsion is useful in imparting water-resistance to thegypsum product. While certain embodiments and best mode of the presentinvention are described herein, these embodiments are merelyillustrative. It will be apparent to those skilled in the art thatmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. An emulsion useful in providing water-resistance to a gypsum product,comprising: at least one wax; an alkyl phenol; polynaplithalensulfonicacid; an alkali metal hydroxide; water; and a complexed starch; whereinthe alkyl phenol is a C₂₄-C₃₄ polymerized methylene-coupled alkylphenol.
 2. The emulsion of claim 1 wherein the alkali metal hydroxide isselected from the group consisting of sodium hydroxide and potassiumhydroxide.
 3. The emulsion of claim 1 wherein the complexed starch is acomplex or a starch and a complexing agent selected from the groupconsisting of a borate compound, a molybdate compound and a molybdenumcompound.
 4. The emulsion of claim 3 wherein the complexing agent issodium tetraborate decahydrate.
 5. The emulsion of claim 3 wherein thestarch is selected from the group consisting of unmodified starch,acid-modified starch, hydroxyethylated starch, oxidized starch, andcationic starch.
 6. The emulsion of claim 3 wherein the starch isacid-modified starch.
 7. The emulsion of claim 3 wherein the ratio ofthe complexing agent to the starch on a weight per weight basis is fromabout 1:4 to about 1:20.
 8. A method for making an emulsion useful inproviding water-resistance to a gypsum product, comprising the steps of:(a) at least one wax and an alkyl phenol to provide a first pre-mix; (b)mixing polynaphthalenesulfonic acid, an alkali metal hydroxide, water,and a complexed starch to provide a second pre-mix; (c) combining thefirst pre-mix and the second pre-mix to provide a mixture; and (d)homogenizing the mixture; wherein the alkyl phenol is a C₂₄-C₃₄polymerized methylene-coupled alkyl phenol.
 9. The method of claim 8wherein the alkali metal hydroxide is selected from the group consistingof sodium hydroxide and potassium hydroxide.
 10. The method of claim 8wherein steps (a) and (b) further comprise heating the first pre-mix andsecond pre-mix to a temperature range of about 185° F. to about 195° F.11. The method of claim 8 wherein step (d) is carried out at a pressureof at least 3500 psi.
 12. The method of claim 8 wherein the complexedstarch is a complex of a starch and a complexing agent selected from thegroup consisting of a borate compound, a molybdate compound and amolybdenum compound.
 13. The method of claim 12 wherein the complexingagent is sodium tetraborate decahydrate.
 14. The method of claim 13wherein the starch is selected from the group consisting of unmodifiedstarch, acid-modified starch, hydroxyethylated starch, oxidized starch,and cationic starch.
 15. The method of claim 13 wherein the starch isacid-modified starch.
 16. The method of claim 13 wherein the ratio ofthe complexing agent to the starch on a weight per weight basis is fromabout 1:4 to about 1:20.
 17. An emulsion useful in providingwater-resistance to a gypsum product, comprising; at least one wax in anamount of about 25% to about 40% by weight based on the total weight ofthe emulsion; a saponifiable wax in an amount of about 2.5% to about4.5% by weight based on the total weight of the emulsion; an alkylphenol in an amount of about of about 0.25% to about 10.0% by weightbased on the total weight of the emulsion; a polynaphthalenesulfonicacid in an amount of about 0.25% to about 5.0% by weight based on thetotal weight of the emulsion; water in an amount of about 55% to about65% by weight based on the total weight of the emulsion; an alkali metalhydroxide in an amount or about 0.5% to about 1.5% by weight based onthe total weight of the emulsion; and a complexed starch, in an amountof about 1.5% to about 3.5% by weight based on the total weight of theemulsion, the complexed starch comprising a starch and a complexingagent selected from the group consisting or a borate compound, amolybdate compound and a molybdenum compound, the starch and thecomplexing agent having a ratio, by weight, of about 4:1 to about 20:1;wherein the alkyl phenol is a C₂₄-C₃₄ polymerized methylene-coupledalkyl phenol.
 18. A gypsum product comprising gypsum and the emulsion ofclaim
 1. 19. A gypsum product comprising gypsum and the emulsion ofclaim
 17. 20. A method for imparting water-resistance to a gypsumproduct comprising the addition to a gypsum product of an emulsion ofclaim
 1. 21. A method of imparting water resistance to a gypsum productcomprising the addition to a gypsum product of an emulsion of claim 17.